1. Field of the Invention
This invention relates to an improvement of a thread chain sewing apparatus having a back tuck function in which when overedging a fabric material, a cut off thread chain is automatically sewn in the first area of a seam of the fabric material, and more particularly to a thread chain sewing apparatus for use in an overedge sewing machine.
2. Prior Art
The thread chain sewing apparatus having a back tuck function to which this invention applies is generally used for consecutive overedging of a lower sleeve edge of some outer wear or the like, and the thread chain formed consecutively from the fabric end on which the overedging has been applied can be sewn in the first area of the seam of a new fabric without manual operation. The fundamental thought of the apparatus of this kind was already proposed in U.S. Pat. No. 4,220,105, and the apparatus according to said Patent has a feature in its positioning device for sewing the thread chain in the leading area of the seam of an oncoming fabric segment after cutting off the thread chain from the fabric segment on which overedging has completed.
In particular, said positioning device for cutting off the thread chain comprises a thread chain cutter equipped with a suction tube having a cutting knife supported near the free end of a finger of a presser and an orientation device operated by a draft tube, a grasping device equipped with a grasping blade and a suctional positioning tube, and a recessed groove extending on a throat plate between the finger of a presser of the throat plate and the grasping device. The thread chain is suctionally induced into the suction tube and after being cut off from the fabric on which the overedging has been completed, the thread chain is discharged to the grasping device by air blow through the draft tube, to be induced into the positioning tube of the grasping device. And at the same time, by moving the grasping blade up and down the thread chain is inserted into said groove so as to be positioned while being grasped by the grasping blade.
In the aspect of the actual operation of the foregoing conventional device, there exist several disadvantages as follows.
In the first place, when the thread chain is sewn in the fabric, it is inserted into the groove formed on the throat plate so as to be positioned on the lower side of a new fabric being moved over the throat plate. In this step, however, because of the construction or structure of the throat plate, said groove cannot be extended up to the needle location. Accordingly a problem of friction with the fabric exists, which affects retention of the thread chain and is not sufficiently overcome or solved, resulting in rather lower and limited efficiency of the sewing operation.
In the second place, since the thread chain is located on the lower side of the fabric, it is sewn blindly by the operator. Accordingly another problem exists in the difficulty of confirming whether the seam formation is adequately carried out or not during the operation, resulting sometimes in defective or non-conforming product having a skipped stitch or the like.
In the third place, since the thread chain is discharged by air blow of the draft tube after being caught by the suction tube and is received by the grasping device located relatively distant thereto, to be inserted into the groove of the throat plate, the position on which the thread chain is held is apt to be unstable, resulting in the difficulty of adequate positioning of the thread chain within the groove.